Concrete Cover Depth Research Articles

Research on quantitative design methods for the durability of reinforced concrete structures in a hot ocean environment

This paper establishes a quantitative design method for the durability of concrete structures in cross-sea bridges through investigation, rapid chloride migration coefficient method (RCM) and theoretical calculation, considering the impact of temperature on chloride ion diffusion rates in a hot marine salt erosion environment. Combined with the RCM test and bridge service data, a quantitative design method for bridge concrete durability is proposed. Test results show that the growth rate of the chloride ion diffusion coefficient of concrete is approximately 1.028 for every 1 °C increase. For every 5 °C increase, the growth rate of the chloride diffusion coefficient of concrete is about 1.15, and the cover depth of the concrete structure should be multiplied by a coefficient of 1.07. Therefore, the concrete cover depth should be appropriately increased, considering the influence of ambient temperature. Furthermore, fly ash, slag, and stone powder can increase the concrete’s resistance to chloride corrosion. When the influence of temperature on the chloride ion diffusion coefficient is considered, the durability design of the concrete structure of the sea-crossing bridge is conducted, which is beneficial for ensuring their service life.

Effects of structural configuration on perforation/spalling damage and secondary fragment velocity of reinforced concrete slabs subjected to close-in explosion

Reinforced concrete (RC) slabs are vulnerable to localized damage from close-in TNT explosions, suffering perforation and extensive spalling damages that generate high-velocity secondary fragments posing severe risks to nearby facilities and personnel. Current numerical methods such as the Finite Element Method (FEM) face challenges in accurately predicting fragmentation due to mesh distortion caused by large deformations and discontinuities, underscoring the need for enhanced modelling techniques. As a result, although numerous studies have numerically investigated how structural configurations influence RC slab damage under blast loads, the issue of mesh distortion and element erosion in FEM has led to the inability in reliably predicting the associated threats from high-velocity fragments. This study numerically investigates the influences of structural configuration (e.g., concrete strength, reinforcement ratio and layout, dimensions of slabs, and concrete cover depth) on the perforation/spalling area and fragment ejecting velocity of one-way RC slabs subjected to close-in explosions through an ALE-FEM-SPH numerical model, which has been demonstrated effective and reliable in the authors’ previous studies. The results indicate that concrete strength and slab thickness most significantly affect both the damage and fragment characteristics, while the slab's width-to-height ratio, reinforcement ratio, and layout, have less influence, particularly on fragment velocity. Empirical equations derived from extensive numerical data are provided to help engineers and security personnel quickly evaluate the blast effects on RC slabs. The accuracy and robustness of the proposed formulae, which can be straightforwardly used to predict blast fragments of reinforced concrete slabs, have been statistically evaluated and the proposed formulae demonstrate satisfactory precision, with less than 20 % error in estimating damage area, maximum fragment velocity, and total kinetic energy of fragments.

An activation guideline for the resistive heating process of iron-based shape memory alloy embedded in concrete

In new and existing reinforced concrete (RC) structures, extensive research has proven that iron-based shape memory alloys (Fe-SMA) can be used as prestressing materials. As for the Fe-SMA embedded in concrete, the resistive heating method is usually adopted to activate its shape memory effect to develop prestress in the concrete. The prestressing process of the Fe-SMA involves multiple physical fields such as electric currents, temperatures, and mechanics. An accurate and standardized implementation of the activation process is essential for the Fe-SMA to effectively generate the expected prestress in the structure. However, data drift can occur when thermocouples measure the temperature of the Fe-SMA through which current flows and non-contact heat sensors can not measure the temperature of the Fe-SMA embedded in the concrete. It is also difficult to theoretically estimate the activation time and temperature of the Fe-SMA in concrete. The pre-test or empirical values are usually required to estimate the activation current and time for reaching the target temperature, compromising the construction efficiency. Additionally, the selection of activation parameters varies wildly for Fe-SMA with different specifications and sizes. There are currently no standardized guidelines for the electrical resistive activation of the Fe-SMA. Therefore, a multi-physical finite element model was developed to study the self-prestressing process of the Fe-SMA embedded in concrete and predict the temperature distribution and prestress of the Fe-SMA and concrete. The effects of the current density, the Fe-SMA shape and size, and the concrete cover depth were analyzed. In the end, an activation guideline for the electrical resistive heating of the Fe-SMA was offered to facilitate the construction and activation process in field engineering.

Experimental study on improving the fire performance of the concrete beams with Fe-SMA

The conventional approach to satisfying the fire resistance requirements in designing reinforced concrete (RC) structures is to ensure enough concrete cover depth for the steel reinforcements. The objective is to prevent the temperature of steel reinforcements from rising too quickly. However, excessive concrete cover depth may increase the risk of concrete spalling during a fire and lead to a larger crack width. Fire is a natural heat source that can activate the shape memory effect of iron-based shape memory alloys (Fe-SMA) to generate recovery stress. This study proposes a new active approach for improving the fire performance of RC structures based on the Fe-SMA. The main objective is to investigate the feasibility of improving the fire performance of RC structures through the recovery stress generated by Fe-SMA under fire. The fire test of nine Fe-SMA RC beams was conducted. The temperature profile in the furnace was similar to ISO834, and the maximum temperature exceeded 800 °C. The flexural behavior of the concrete beams reinforced with Fe-SMA during and after the fire was tested. The experimental results demonstrate that the Fe-SMA has great potential in improving the fire performance of RC structures. The mid-span deflection of the Fe-SMA RC beams under fire is significantly lower than the conventional RC beams. The fire resistance of Fe-SMA RC beams increases from 97 min to 133 min at load level 0.3 and from 69 min to 103 min at load level 0.5. The residual deformation of Fe-SMA RC beams reduces from 46.3 mm to 27.6 mm at load level 0.3 and from 34.7 mm to 19.8 mm at load level 0.5. In addition, after 1 h of fire exposure, the Fe-SMA can develop permanent prestress after the beam cools to room temperature, improving the mechanical properties after fire. The residual bearing capacity and residual stiffness of the Fe-SMA RC beams are 21% and 86%–121% higher than the conventional RC beams, respectively. The prestress generated by Fe-SMA after 1 h of fire exposure was estimated using the equivalent section method.

Bond behavior and anchorage length of 18-mm-diameter steel strands embedded in ultra-high-performance concrete: an experimental and analytical study

The combination of large-diameter steel strands and ultra-high-performance concrete (UHPC) presents a promising opportunity to improve the performance of prestressed concrete structures. However, investigations on the bond between them, which determines important design parameters such as the anchorage length of the strand, are insufficient. This study performs pull-out tests of 18-mm-diameter steel strands embedded in UHPC to investigate the bond property. The test data is analyzed to determine the effects of embedment length, concrete cover depth, and stirrup ratio on the bond property. Based on the analysis, a bilinear bond-slip model is calibrated following the principle of energy equivalence. Moreover, an empirical formula for the maximum bond stress is proposed. According to the obtained bond properties, the anchorage length of the strand is evaluated using the approximate probability method, and the results are comparable with the values given in several design codes.

Uniaxial tensile behavior of half-grouted sleeve connections with concrete cover after exposure to elevated temperatures

This study presents the tensile behavior of a half-grouted sleeve connection (HGSC). A total of 15 prism samples of grout are subjected to a series of tests before and after exposure to various temperatures. A total of 75 eccentric HGSC specimens with a 40 mm concrete cover and 15 central HGSC specimens without a concrete cover were fabricated for uniaxial tensile loading tests. A pseudo-transient heating regimen was applied to HGSC specimens with concrete covers; the specimens were heated to the desired temperature and left there for a duration of 0 min. This study systematically investigates the tensile properties of post-fire HGSC specimens to assess the combined effects of peak environmental temperature (20 °C, 200 °C, 400 °C, 600 °C, 800 °C), concrete cover depth (0 mm, 40 mm), concrete strength grade (C30, C35, C40, C45, C50), and concrete spalling (burst or unburst). The failure mode, load–displacement curves, sleeve strain distribution, and heat transfer are employed to characterize the response of the HGSC specimens, which is subsequently discussed. It is discovered that, although concrete compressive strength plays a minor role, temperature, concrete cover, and explosive spalling significantly influence certain post-fire tensile parameters of the HGSC. Based on the results, there is considerable potential for determining the ultimate tensile force in HGSC specimens with concrete covers and the remaining compressive strength of grout using ultrasonic pulse velocity detection. Furthermore, a comparative accuracy analytical model, incorporating the influence of tangential strain derived from the experimental results, is established based on confinement stress.

A Non-destructive Method for the determination of Carbonation Time for Nominal Concrete Cover Depth Using Non-Linear En-semble Prediction

Carbonation, a process involving the reaction of carbon dioxide and moisture, results in the for-mation of powdery calcium carbonate, a critical durability issue causing reinforcement corrosion. The study analyzed carbonation data from coastal and inland buildings in the Turkish Republic of Northern Cyprus, re-vealing higher carbonation rates than anticipated within their lifespan. An artificial intelligence model named Support Vector Machine (SVM) was applied to predict carbonation time (T) to penetrate concrete cover of 25mm in the TRNC. Subsequently used two ensemble techniques, namely Neural Network Ensembles (NNE) and Support Vector Machine Ensembles (SVME) to enhance the performance of the prediction of T. Four performance criteria namely Correlation Coefficient (CC), Root Mean Square Error (RMSE), Correlation Co-efficient (R2), Mean Absolute Error (MAE) was applied to verify the modelling accuracy. The Values of R2 of Ensemble techniques indicated significant increase in the performance, greater than the SVM model. This shows that using ensemble techniques is promising in getting better predictions of carbonation time (T) to penetrate concrete cover. The results obtained showed that NNE and SVME combination demonstrated the best performance under the evaluation criteria of R2 = 0.8721 and R2 = 0.8644 in testing phases respectively in comparison SVM-M1 to SVM-M3.

Service Life Design of Concrete Structures Made of High-Volume Limestone Powder Concrete—Case of the Carbonation-Induced Corrosion

One of the paths to CO2 emissions reduction in the concrete industry is to use low-clinker cements, providing at the same time the performance of concrete that is adequate for application in concrete structures. This paper explores the impact of the clinker replacement with high amounts of limestone powder (21–70% in the powder phase) on concrete carbonation resistance. To quantify this impact, the empirical relationship between the carbonation resistance and the compressive strength of the high-volume limestone powder concrete (HVLPC) was established. For that purpose, the regression analysis was applied on the experimental results collected from the published research. The service life analysis based on the full probabilistic approach was performed using the fib Model Code 2010 prediction model and proposed empirical relationship. The first-order reliability method (FORM) was applied to solve the limit state function of reinforcement depassivation with a reliability index equal to 1.3. The obtained minimum concrete cover depths were 40–110% higher compared to those prescribed in the current European standard EN 1992-1-1:2004 for indicative strength classes. Based on the full probabilistic analysis, recommended cover depths are given for all carbonation exposure classes, commonly applied concrete strength classes, and service lives of 50 and 100 years.

Determining the Location of Steel Reinforcement in Thick Concrete Walls by Non-Destructive Inspection

Abstract Concrete cover is the thickness of the concrete layer that protects the reinforcing steel bars (rebar) within a reinforced concrete structure. It acts as a barrier against external elements such as moisture, chemicals, and environmental factors, safeguarding the rebar from corrosion. Concrete cover measurement is performed by using various nondestructive tests such as GPS (Ground Penetrating Radar), electromagnetic test and ultrasonic. The main benefit of the concrete cover thickness measurement is to explain the causes of corrosion and identify areas that have the capability to corrode faster. This paper discusses the possibilities to measure the concrete cover depth and determine the location of steel bars of a thick-walled concrete structure by using different nondestructive testing methods. The methods studied are a concrete cover meter, Ground Penetrating Radar, which is based on propagation radar waves in concrete, and Ultrasonic Pulse Echo tomography based on stress waves produced by ultrasonic pulses. The paper demonstrates the use of these methods for in-situ measurements on a thick-walled reinforced concrete structure. The concrete cover depth and the location for the reinforcement bars received by different methods are compared and the strong and weak points of the methods are discussed. The results indicate that the concrete cover meter is suitable for measuring the thickness of concrete cover, while the Ground Penetrating Radar and the Ultrasonic Pulse Echo device were able to identify and locate the reinforcement bars position in the concrete structure.

Modeling of bidirectional chloride convection-diffusion for corrosion initiation life prediction of RC square piles under drying-wetting cycle

Modeling chloride penetration mechanism in unsaturated concrete is essential for corrosion initiation life prediction of marine reinforced concrete (RC) structures. This paper presents a bidirectional chloride convection-diffusion model for the chloride concentration distribution of RC square piles in the tidal and splash zone. The finite difference numerical method is used to solve the convection-diffusion governing equations with the drying-wetting cycle. The numerical model is validated by two experimental results and the analytical solution with constant surface chloride conditions. The peak value and convection depth in the chloride distribution curve of RC square piles are investigated. The results show that the periodic drying-wetting chloride environment is the dominant factor of the convection effect formed in the surface layer of the square piles. Moreover, a coupling effect is observed in the diagonal areas of square piles. The corrosion initiation life under a periodic drying-wetting chloride environment is shorter than that with constant surface chloride concentration. Furthermore, the sensitivity analysis results show that the diffusion coefficient, the concrete cover depth, and the variable rate of drying-wetting cycles are the critical parameters for predicting the corrosion initiation life of RC square piles under the drying-wetting cycle.

Experimental study with DIC technique on the bond failure of structural concrete under repeated reversed loading with different amplitude

The bond between deformed steel rebar and concrete plays a critical role against seismic action, thus it is important to capture the dynamic bond loss and establish the bond-slip model with cyclic loading. To explain the macroscale performance such as bond-slip relationship and establish the bond strength model, it is meaningful to capture the mesoscale and local behaviors between ribs and concrete. In this paper, pull-out specimens with rebar embedded in concrete and small windows excavated in the cover concrete are adopted with DIC technique to monitor the strain variation and crack development along the interfaces under static and reversed loading of different amplitude. From the test, it is found that DIC is an effective approach to obtain the localized characteristics including the normal and shear deformations. Through parametric study, the effects of concrete cover depth and the existence of stirrups on bond deterioration in terms of both global and local behaviors are studied. Interestingly, the global slip and local crack-width show synchronically increase under the pulling-out action, which demonstrates that the macroscale behaviors could be clarified from mesoscale measurement with the aid of DIC technique.

Flexural behavior of long-term loaded RC beams strengthened by ultra-high performance concrete

This study aims to investigate the flexural behavior of reinforced concrete (RC) beams strengthened with ultra-high-performance concrete (UHPC) after being loaded with long-term sustained loads for more than 20 years. Seven RC beams, originally fabricated in 1998, are categorized as the one-time pouring unnotched beam (Overall beam), one-time pouring notched beam (Notched beam), and two-time pouring beam (Repaired beam). These RC beams were firstly tested under the effect of long-term sustained loads which lasted 23.6 years. Subsequently, notched beams were strengthened using UHPC (hereafter named as Strengthened beam), which are tested under four-point bending test to investigate the significance of strengthening using the UHPC. Long-term load effects on the flexural performance of RC beams, including creep, cracking, concrete carbonization, and steel rebar corrosion were tested and analyzed. Test results showed that the maximum carbonization depth was less than the concrete cover depth and the steel rebars corrosion was among 1.51–2.47%, which indicates that the steel rebars inside the beam are well protected and are almost free of rust. The bearing capacity of the strengthened beams were increased by 24.6–48.6% compared with that of the Notched beam, which emphasizes the significance of strengthening using the UHPC. The displacement ductility of the strengthened beams was decreased by 82–94% compared with that of the Overall beam, however no brittle failure was observed during the test. It is worth mentioning that the internal changes, caused by the long-term sustained loading, could not be completely changed by adopting UHPC strengthening, while the stiffness reduction caused by long-term loading considerably influenced the flexural behavior of the UHPC strengthened beams. In addition, more attention shall be paid to the UHPC-NC vertical interface which remarkably affected the flexural performance of the Strengthened beams.

Evaluation of the Bond Shear Strength and Corrosion Resistance of Concrete with Setting Retarder

In this study, the bond shear strength and corrosion resistance of concrete with setting retarders were evaluated. For this, slant shear, bi-surface, and accelerated corrosion tests were conducted. The variables considered included the proportion of the setting retarder (0 and 1%), surface treatments of concrete (as-cast, chipping, and brushing), curing hours (8, 16, and 24 h), and concrete cover depths (20, 30, and 45 mm). Consequently, the bond shear strength of concrete with the retarder showed a higher value than that of normal concrete. Moreover, an increase in curing hours resulted in a higher value of the bond shear strength. Furthermore, the addition of a retarder in concrete increased corrosion resistance. Based on the test results, the addition of a setting retarder is believed to be a suitable solution to address the bond shear strength and durability issues that may arise at the interface of delayed concrete placement.

Experimental and Numerical Study on RC Beams Strengthened by NSM Using CFRP Reinforcements

Near Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP) reinforcement technique to improve the flexural strength of reinforced concrete members has become increasingly attractive in recent years. In this study, the practical problem of concrete cover depth cutting limitation was investigated. Twelve specimens were tested by four-point bending until failure. Experimental parameters include concrete cover depth, CFRP reinforcement type, CFRP positioning, and stirrups status. Furthermore, a nonlinear FEA model was developed to simulate the tested beams and was able to predict the experimental behavior satisfactorily. A series of parametric studies were then performed using this model to understand the effect of various reinforcement parameters on the flexural performance of the beam. The results showed that Strengthening with CFRP resulted in a significant increase in yield and ultimate strengths, but a significant ductility loss was recorded due to CFRP strip debonding in the strengthened beams, this problem was addressed by using more efficient strengthening techniques utilizing the effective bond length and a proper groove depth and positioning for the NSM bars.

Prediction of the Moment Capacity of FRP-Strengthened RC Beams Exposed to Fire Using ANNs

In this study, an Artificial Neural Network (ANN) model to predict the moment capacity of Fiber Reinforced Plastic (FRP) strengthened Reinforced Concrete (RC) beams exposed to fire is developed. The software ABAQUS heat transfer analysis is verified by comparison with the fire resistance test results. Through this heat transfer analysis, the temperature distribution of the beam section is determined, and 400 datasets are obtained using the moment capacity calculation method combined with the section equilibrium method. The data consist of eight input parameters: the beam width, beam height, FRP area, rebar area, concrete compressive strength, insulation thickness, concrete cover depth, and fire exposure time. The output parameter is the moment capacity. The ANN model is developed through a sensitivity study using the algorithm type and the number of hidden-layer neurons as variables. The average error between the predicted data of the developed ANN model and the target data obtained from the moment capacity calculation method was 0.35 kN·m, and the average relative error was 0.2512%, showing high accuracy. Therefore, the ANN model developed here can determine the moment capacity without complex calculations. The effects of the input parameters on the moment capacity of the FRP-strengthened RC beams exposed to fire are investigated using the ANN model.

Service life prediction of reinforced concrete structures subjected to corrosion: a comparative study

PurposeReliable estimations of the extent of corrosion and time required to reach specific safety limits are crucial for assessing the reliability of aging reinforced concrete (RC) bridges. Engineers and decision-makers can use these figures to plan suitable inspection and maintenance operations.Design/methodology/approachAnalytical, empirical and numerical approaches for estimating the service life of corroded RC structures were presented and compared. The concrete cover cracking times, which were predicted by the previously proposed analytical models, were compared with the experimentally obtained cracking times to identify the model/s for RC bridges. The shortcomings and limitations of the existing models are discussed.FindingsThe empirical models typically depend on the rate of corrosion, diameter of steel reinforcement and concrete cover depth and based on basic mathematical formula. In contrast, the analytical and numerical models contain the strength and stiffness properties of concrete as well as type of corrosion products and incorporate more complex mechanical factors. Four existing analytical models were analyzed and their performance was evaluated against existing experimental data in literature. All the considered analytical models were assumed thick-walled cylinder models. The maximum difference between observed cracking time from different test data and calculated cracking time using the developed models is 36.5%. The cracking times extend with increase in concrete cover and decrease with corrosion current density. The development of service life prediction models that considers factors such as heterogeneity of concrete, non-uniform corrosion along rebar, rust production rate and a more accurate representation of the corrosion accommodating region are some of the areas for further research.Research limitations/implicationsOutcome of this paper partially bridge the gap between theory and practice, as it is the basis to estimate the serviceability of corrosion-affected RC structures and to propose maintenance and repair strategies for the structures. For structural design and evaluation, the crack-width criterion is the greatest practical importance, and structural engineers, operators and asset managers should pay close attention to it. Additionally, repair costs for corrosion-induced serviceability failures, particularly concrete cracking and spalling, are significantly higher than those for strength failures. Therefore, to optimize the maintenance cost of RC structures, it is essential to precisely forecast the serviceability of corrosion-affected concrete structures. The lifespan of RC structures may be extended by timely repairs. This helps stake holders to manage the resources.Practical implicationsIn order to improve modeling of corrosion-induced cracking, important areas for future research were identified. Heterogeneity properties of concrete, concept of porous zone (accommodation effect of pores should be quantified), actual corrosion morphology (non-uniform corrosion along the length of rebar), interaction between sustain load and corrosions were not considered in existing models. Therefore, this work suggested for further researches should consider them as input and develop models which have best prediction capacity.Social implicationsThis work has positive impact on society and will not affect the quality of life. Predicting service life of structures is necessary for maintenance and repair strategy plans. Optimizing maintenance strategy is used to extend asset life, reduce asset failures, minimize repair cost, and improve health and safety for society.Originality/valueThe degree of accuracy and applicability of the existing service life prediction models used for RC were assessed by comparing the predicted cracking times with the experimentally obtained times reported in the literature. The shortcomings of the models were identified and areas where further research is required are recommended.

Theoretical Analysis of Flexural Time-Varying Properties of Aluminum Alloy-Reinforced RC Beam under Atmospheric Environment

This paper aims to reveal the degradation of the flexural load capacity of reinforced concrete (RC) beams reinforced with aluminum alloy (AA) under atmospheric conditions. For the same, first, time-varying models of the flexural load capacity of RC beams were developed before and after reinforcement with AA and steel plate based on the time-varying properties of the materials. Subsequently, upon collecting existing test data, the reliability of the models was verified. Finally, the parameters of AA-reinforced and steel plate-reinforced RC beams were analyzed to investigate the influence of factors such as concrete cover depth, cross-sectional area of reinforcing material, and cooperative working coefficient of reinforcing material and concrete (demonstrate the ability of reinforcement material and concrete to work together) on the remaining service life, rust initiation time, and cracking time. The results show that under atmospheric environment, the flexural time-varying degradation model for RC beam can be divided into three stages: pre-rusting, rusting-pre-cracking, and post-cracking, with differences in the dominant factors at each stage. In terms of long-term performance, AA reinforcement is significantly more efficient than steel plate reinforcement. This study provides some theoretical basis for the design of AA reinforcement in the atmospheric environment.

Steel Reinforced Self-Compacting Concrete (SCC) Cantilever Beams: Bond Behaviour in Poor Condition Zones

Previous investigations carried out on reinforced self-compacted concrete (SCC) beams have reported contradictory results on reinforcement bond behaviour occurring in the zones defined for good bond conditions according to Eurocode2. Cantilevered SCC beams’ critical upper tension reinforcement bond behaviour has previously had limited reporting. In this study, the bond behaviour in normally vibrated concrete (NVC) and self-compacted concrete (SCC) in poor conditions zones are compared and the differences are highlighted. The effect of four parameters, including (i) concrete type (SCC and NVC), (ii) characteristic strength of SCC, (iii) lap splice length, and (iv) depth of concrete cover for the reinforcement is investigated. It was found that for the studied beams, increasing splice length improved the energy absorption and changed the failure mode to a more ductile manner even at the poor bond conditions zones. The maximum measured steel strains in SCC beams in the lap splice zones, were higher than those for NVC specimens. The mean bond stress values, for SCC beams with 25–50% lap splice lengths, were higher than those of NVC beams, with the same lap splice lengths, by 16–13%, respectively. The results of the current study showed that the empirical equations from the literature overestimated the bond strength of the splice lap length for cantilever upper steel in SCC beams with long splices which agrees with the state of the art as these equations were developed originally for short anchorage lengths.

Evaluating the Impact of Concrete Design on the Effectiveness of the Electrochemical Chloride Extraction Process.

This paper presents a simple comparative method for evaluating the impact of concrete design on the effectiveness of repair with the electrochemical chloride extraction (ECE) process of reinforced concrete structures. This comparison covered two concretes with different types of used cement. Penetration of chloride ions to induce corrosion processes was accelerated with the electric field. However, the corrosion process itself occurred naturally. When the corrosion process was found to pose a risk to the reinforcement, the profile of chloride ion concentration was determined at the depth of concrete cover. Corrosion current intensity during migration and extraction processes of chloride ions was measured with the LPR method. Then, this serious condition for the structure was repaired with electrochemical chloride extraction. Rates of chloride extraction were determined from the derived concentration profiles. It should be noted that the critical concentration Ccrit = 0.4% at the rebar surface was reached after 21 days of the migration process. Moreover, after the same time of extraction, the concentration was reduced by 95% at the rebar surface, which could suggest that extraction rate was slower than chloride ion migration to concrete within the electric field. Using the migration coefficient for predicting the extraction time, as well as ignoring the variability of the extraction coefficient and the initial concentration over time, may result in too short or unnecessarily long extraction times.

Automated Geometric Quality Inspection of Rebar Layout using RGBD Data

Quality control and quality assurance during construction is vital to ensure the structure is built as designed and durable. For reinforced concrete (RC) structures, rebar diameter, spacing, and concrete cover depth are critical in ensuring that the structure is designed for adequate strength and can maintain its service life without unplanned interventions. Once the rebar is laid out in the field, construction inspectors do the required quality control to ensure that the constructed rebar mat matches the design documents. The checks are made at finite points and thus can be improved with currently available technologies such as LiDAR, augmented reality (AR), and uncrewed aerial vehicles (UAVs). This paper summarizes the available technologies for such an effort and focuses on using Red Blue Green Depth (RGBD) cameras as a quality control tool for construction inspection of RC structures such as buildings and bridges. A study conducted using an RGBD camera for estimating rebar diameter is presented in this paper. Results show that RGBD cameras have a very high potential as a low-cost, efficient tool for quality control of RC structures during construction. RGBD cameras can potentially augment current visual inspections in assuring the structures are built as per design drawings, meeting the appropriate specifications with acceptable accuracy.